Acoustic device



. tively large central 0 prisesa Patented Junel3, 1933 UNITED v s'rATss PATENT orrlcs DUAL H. BEDELL, 01 am,

I" was. AS81030! TO BILL TELEPHONE LABORA- IQBIIB, INQOBPOMTED, m roux. I.

Y, A CORPORATION 01' m You aoous'rrc mw'rcit I Application and larch :1, 1m. Serial 1r..m,11s.

This invention relates to acoustic apparatus and particularly to a directional baifle, or shield, for use with sound recelving devices.

An object of the invention is to provide a directive sound baflle of sound absorbing -ma-- terial for shielding sound receiving devices against reflected and extraneous sound.

- In accordance with one feature of the'invention the absor tion power ofthe walls of the bafle, or shie d, is approximately unit for frequencies above 100 cycles per secon In one embodiment of the invention there is provided a horn-like sound baflle or screen for sound receiving devices having sound absorbing walls comprising a plurality of unevenl materia Specifically, the invention provides a sound shield for sound receivers having a sound absorbing wall comprising a' mu t1 Elicity of unevenly spaced layers of cloth.

aving a total thickness of approximately ,4 the wave length of the lowest frequency to be absorbed.

Referring to the drawing; Fig. 1 is a perspective view partly in secbafiie for microphones in accordance with the invention;

' I Fig. 2 shows a detail of construction; Fig. 3 shows the fr uency characteristics of a wer absor tion versus afie in accor ance with the invention; and

Fig. 4 illustrates diagrammatically a use the device in connection with sound picture recording.

In eral appearance the bafie, in the merit shown in the drawing, is cylindrical with a longitudinal conical passage therethrough. It consists of a skeleton or lattice framework on which the sound absorbing material is arranged ashereina fterdescribed. One end of the framework complurality of radially extending strips 6 0 mix suitable material, such as wood, connecte together at their inner ends by light cord members 7 leaving a comparanected together at their outer ends by similar members 9. The frame at the opposite smaller than opemng spaced layers of sound absor ing' here 14 8 and also con-.

end is similar in connected at their outer ends by cord members 11 and secured to-.

gether at their inner ends by an annular disc 12 leaving an opening 13 substantially 8. Joining the outer ends of the radial members 6 and 10 are lon itudinal strips 14 which define practica y a cylindrical surface and joining the inner end of the same radial members 6 and 10 are longitudinal strips 15 which define a conical surface. Secured to the inside-of the frame to members 6 is a disc shaped pad 16, of rock wool or other suitable material, havmg a central op g therein corresponding to opening 8, and sup orted on the opposite end is a similar pa 17 having a central opening therein correspond to openin 13. A. pad, or lining, 18 of similar'souni' abmrb' material is also secured to memormmg with the end pads. 16 and 17 an annular c amber' wherein are stretched between the pad 16 and 17 a plurality of concentric sto-conical' walls, or layers of cloth 19 and 20, the innermost, layer 0 which defines a conical sound receiving chamber. These walls are supported by wires 22, in the he'ms 23 thereo stapled to In the em the radial members 6 and 10a bodiment shown in the drawing there arenineteen walls, or layers of'cloth, the inner seven lgyers 19 of which are muslin having a mass 0 approximately .018 per square centimeter and an acoustic resistance of approximately 6 ohms per square centimeter and the outer twelve layers 20 of which are canton flannel having a mass of approximately .017 per square centimeter and an acoustlc'resistance of approximately 12ohms' r square centimeter.

The spacing ween the walls is varied mcrea'si outwardly for aboutthe first seven and endecreasing. The overall' -dimansions of a suitable structure is approximt'gtely three feet long and six feet in diame r.

represents the absorption .'of a ae- In Fig. 3 is shown atypical curveA which well-known material. It will be noted that the absorption for the structure in accordance with the invention is practically unity for all frequencies above 100 cyc es per second. This type of bafile has a very high directive selectivity since it absorbs substantially all sounds outside of the solid angles subtended by the opening therein.

Fig. 4 represents graphically an application of the invention to sound picture recording. The microphone 25 is supported in the small end of the sound receiving bafile 26 by any suitable means, not shown, and a second bafile 27 of suitable material depends from the front of bafie 26. Baille 27 has a window of glass 28 tor the picture machine. With this combination of bafiles it is unnecessary to either damp the studio walls or to enclose the picture machine in a sound proof booth for only sounds reaching the microphone directly or reflected from surfaces within the solid angle subtended by the opening in the baflie 26 are transmitted, all

' other sounds impinge on the baflle and are absorbed. If h is the height of the speaker or some source above the floor then (Z is the distance the source can move to and fro in the efiective area of the baifle and still prevent the sound from being reflected from the floor to the transmitter. Obviously this may be made relatively large. Qne great advantage of the invention therefore is that y it permits artists to perform in acoustic surroundings and with the same freedom of movement to which they are accustomed for binaural listening.

What is claimed is:

1. A directive sound baflle for a sound receiving device comprising a tubular sound duct open at one end for receiving sound to actuate a sound receiver at the other end,

said duct consisting of a plurality of substantially concentric layers of non-resonant material spaced to form a multiplicity of chambers therebetween.

2. A directive sound bafile in acco dance with claim 1, characterized in this that the layers are unevenly spaced transversely.

3. A directive sound bafile in accordance with claim 1, characterized in this that the layers are unevenly spaced, the spacing increasing inwardly.

4. A directive sound bathe in accordance with claim 1, characterized in that the layers are. unevenly spaced, the spacings increasing outwardly. I

5. A directive sound baflle in accordance I with claim 1, characterized in this that the spacing increases outwardly and inwardly from a medial layer.

6. A directive sound baflle in accordance with claim 1, characterized in this that the thickness of the wall is approximately one quarter the wave length of the lowest frequency to be absorbed.

7. A directive sound bafile in accordance with claim 1, characterized in this that the layers are substantially pyramidal of different slopes. I

8. A directive sound baille in accordance with claim 1, characterized in this that the layers have different slopes increasing outwardly, the exterior layer having a substantially constant cross-section. v 9. A directive sound bafile in accordance with claim 1, characterized in this that the elements have different coefiicients of absorption.

10. A directive sound bathe in accordance with claim 1, characterized in this that the elements are cloth.

11. A directive sound oafile for a sound receiver comprising sound absorbing walls forming a conduit tapering from an open ing at one end to a relatively larger opening at the other, said walls being substantially thicker at the ends having the smaller opening.

12. A directive bafile for a sound receiver comprising a plurality of tubes of cloth. a wire frame secured to the ends of each tube and means associated with said wire frames to support said tubes in concentric relation.

13. A directive sound baflle for a sound receiving device comprising a tubular sound duct-having a tapered passage open at its larger end for receiving sound to actuate a sound receiver at the smaller end, said duct being defined by a plurality of substantially concentric layers of sound penetrable material separated to form air spaces therebetween.

14. A directive sound bafile for a sound receiving device comprising a tubular sound duct having a multiplicity of nested tubular elements of sound absorbing material, means for supporting said elements in spaced relation to form air chambers between adjacent elements.

15. A directive sound bafile for a sound receiving device comprising a tubular duct having a tapered sound passage open at its larger end for receiving sound to operate a sound receiver at the smaller end, said duct consisting of a plurality of tubular substantially concentric walls of sound absorbing material, means for supporting said walls in spaced relation to form air chambers therebetween, and means for closing the ends of said air chambers without obstructing the sound entrance in said duct.

16. A directive sound baflle for a sound receiving device comprising a tubular duct defining a sound passage open at one end for receiving sound to actuate a sound receiver at the other end, said duct consisting of a plurality of substantially coextensive layers of sound penetrable material sur- ICC rounding said p w: each layer surrounding the adjacent inner layer and means supporting sud layers in spaced relrfion to provide an spaces therebetween.

In witness whereof, I hereunto subscribe Y my name this 9th day of March, 1932.

,EUAL H. BEDELL. 

